Funai said it photographed "strong and healthy" warriors, six huts and an area of crops. It is not known which tribe the group belonged to.

"Four distinct isolated peoples exist in this region, whom we have accompanied for 20 years," Funai expert Jose Carlos Meirelles Junior said in a statement.

Funai does not make contact with indigenous people and prevents invasions of their lands, to ensure total autonomy for the tribes, the foundation said.

There are more than 100 uncontacted tribes worldwide, most of them in Brazil and Peru, said Survival International, a group that works to protect the human rights of tribal people.

Survival International said that the tribes in Brazil are in danger from illegal logging in Peru. They say the logging is driving uncontacted tribes over the Peru border and could lead to conflict with the 500 uncontacted people living on the Brazilian side.

The pictures were taken to counter those who said that there was no one living in the area.

"These pictures are further evidence that uncontacted tribes really do exist," Survival director Stephen Corry said on the group's website.

"The world needs to wake up to this, and ensure that their territory is protected in accordance with international law. Otherwise, they will soon be made extinct."

Fiona Watson, campaign co-coordinator for Survival International, said the tribesmen are likely "fragments" of what was once a much larger group.

"This is an area where there has been rubber extraction, historically, 100 or so years ago. They're probably the survivors of massacres ... who sought refuge deep in the Amazon rainforest for their own safety and protection," Watson told CTV Newsnet on Friday from London, England.

She said the defensive pose struck by the tribesmen, with spears pointed at the air, clearly shows they are defending themselves and are frightened at the sight of the plane above them.

"The message is clearly 'stay away, leave us alone.'"

Watson said contact with outsiders could even be fatal for these tribespeople, who would be vulnerable to diseases.

"These people are very isolated, they have no immunity to common things like the cold and flu and they could die very quickly," Watson told Newsnet

With files from The Associated Press

Photos

This image released by Survival International, shows uncontacted Indians of the Ethno-Environmental Protected Area along the Envira river, in the Brazilian state of Acre, close to the border with Peru, photographed during a flight in May 2008.